Gear shifting transmissions of motor vehicles are generally shifted or controlled by means of an operating device disposed within reach of the driver. Actuating elements such as shift levers or selector levers are used regularly for this purpose, and are located, for example between the front seats of the motor vehicle or in other regions of the cockpit.
In the case of mechanical transmission control or mechanical coupling between the selector lever and the gear shifting transmission—using a cable or linkage for example, the selector lever position always coincides with the actual transmission state due to the mechanical coupling. As a result, the driver can deduce, on the basis of the particular selector lever position, the current gear state of the transmission, and, then he can feel confident that the lever position coincides with the actual gear state of the transmission.
However, when gear shifting transmissions are actuated electrically or using shift-by-wire, the actuating lever in the passenger compartment and the motor vehicle transmission in the engine compartment are no longer mechanically coupled in this manner. Instead, in the case of “shift-by-wire” transmissions, the shift commands are transmitted from the operating device to the motor vehicle transmission using electrical or electronic signals, and the shift commands are then implemented in the transmission using electrohydraulics, for example. Due to the absence of a mechanical connection between the transmission actuator system and the actuating lever, the transmission state, any shift interlocks, or impermissible shift commands can no longer impact the state of the actuating lever directly and noticeably for the driver.
In by-wire actuated gear shifting transmissions, however, the absence of a mechanical connection between the transmission actuator system and the selector lever can, under certain basic conditions or in the case of an error, also lead to the selector lever position no longer coinciding with the gear state of the transmission.
For example, modern automatic transmissions generally include a so-called “Auto-P” function, for example, that ensures that when the driver leaves the vehicle, the parking lock may possibly be engaged automatically in the transmission, for instance to prevent the unattended vehicle from rolling away if the driver failed to engage the parking lock before leaving the vehicle. In other words, the Auto-P function, which particularly can be automatically activated, when the ignition key is removed or the driver leaves the vehicle, ensures that the parking lock is automatically engaged in the transmission, regardless of the gear state that was actually selected using the selector lever. Thus, the parking lock would also be engaged automatically by the Auto-P function of the transmission or the vehicle if the driver had left the selector lever e.g. in the neutral position, in a tip gate that may be present, or in one of the gear selection positions.
In this case however, the selector lever position does not coincide with the actual gear state of the transmission. When the driver returns to the vehicle or at the next attempt to start the vehicle, the position of the selector lever would therefore provide the driver visually and haptically with initially incorrect information. On the basis of his perception of the selector lever position, the driver would have to assume that the transmission is engaged in a neutral position, in the tip mode or in a gear selection position, although the transmission is actually engaged in the parking lock. This discrepancy between the selector lever position and transmission state could therefore lead to undesired operating errors or incorrect conclusions by the driver.
The applicant's document, DE 10 2007 015 262, A1, discloses an operating device for a motor vehicle transmission having a device for selector lever return, which has an actuating device having a gear motor, with which the selector lever can automatically be returned from the manual shift gate (tip gate) into the automatic gate, or the selector lever can automatically be returned into the park lock position, for example. This known operating device is, however, associated with a certain design complexity in order to implement the desired actuating mobility of the selector lever, with the corresponding consequence of construction space and costs. It must also be expected that the electromotive drive and the reduction gear that are present there can generate disruptive noises.
The same applies for the gear shift device for an automatic transmission known from DE 100 05 328, A1. In this gear shift device, a detent element connected to a selector lever is simultaneously in engagement with a notched contour and a ramp that is adjustable by a motor. By means of the ramp, the detent element can be brought out of engagement with the notched contour, and subsequently due to the incline of the ramp—together with the selector lever—can be automatically returned into a specific detent position. The motor or hydraulic drive of the ramp in this known device is, however, also relatively complex and requires considerable construction space. In the case of a drive using an electric gear motor noise problems are also to be expected.